(191as) Zn Recovery from Electroplating Sludge Using Stirred Tank Bioreactor

Electroplating sludge contains various harmful metals such Zn, Cu, Ni, Cr, Fe, etc which is produced from electroplating industries in India. The metals discarded into environment by electroplating industries are in huge amount. Hence, there is a need for the recovery of metals from sludge before it gets discharged into the environment. Bioleaching is one of the suitable method for the recovery of metals from solid waste. The present study deals with the recovery of Zn from electroplating in a lab scale stirred tank bioreactor.

A 20 L capacity stirred tank reactor was fabricated along with other accessories to conduct lab scale pilot plant studies for II batch electroplating sludge. The experiment was started with growing T.ferroxidans culture in 2 L of 9K media. The pH of the media was 2.3. The growth of T.ferrooxidans was observed within 2-3 days. Two liters well grown culture of T.ferroxidanswas added in stirred tank along with 8 L of 9K media having 2.2% (w/v%) of ferrous sulfate (half strength). The pH of the media was adjusted to 6.0 in the beginning of the experiment and 1% (w/v%) of II batch electroplating sludge (100g) was added in stirred tank. Proper mixing was provided through stirrer to the entire mixture. Later, 2 ml of sample was collected in the regular interval of 2 days for the Zn analysis. The total duration of the experiment was 49 days. The experiments were conducted in duplicates and average value was plotted along with time.

It was observed that the concentration of Zn was increased significantly for initial days of bioleaching process and later it became steady. The final concentration of Zn in supernatant was observed as 190 ppm on 49th day of bioleaching process. From the material balance (as per XRF result), the amount of zinc in initial sludge sample and after 49th day of bioleaching process was obtained as 3649 mg and 1900 mg. This shows the 52.06% recovery of Zn from solid sludge. The results obtained in the lab scale stirred tank (52.06%) are in agreement with the results obtained from shake flask studies (56.17%). The final concentration of Zn in solid sludge was estimated as 0.919% through XRF analysis which also match with the results of shake flask studies (Table 6). These results indicate the feasibility of scaling up the bioleaching process from lab scale to pilot or large scale operation.